Look to the sky tonight, as Earth aligns with Mars and the Sun

Tonight, the rover Curiosity may get to see a truly rare event: the closest thing Mars will ever experience to a Terran eclipse. Though we call such an event the Opposition of Mars, this is a typically human-centric view of the universe. Tonight the Earth will move directly between the Sun and Mars, and the resulting view should be spectacular from either planet. From Mars, the Earth should be clearly visible in silhouette — and from our own planet of Earth, Mars will shine brighter than any other object in the sky.

In fact, Mars should be shining up to 10 times brighter than the brightest stars, called first magnitude stars. This means that anyone lucky enough to have clear skies tonight should be able to see the Red Planet shining bright — and large. The Opposition of Mars comes just 6 days before another major Martian event: the convergence of the orbits of Mars and Earth. On April 14th, the orbits of Earth and Mars will be at their closest point, a mere 92 million kilometers apart. Though incredibly close, this near pass pales in comparison to that witnessed in 2003, when Mars passed us at just 55 million kilometres.

If you’re wondering why Mars would be lit up so brightly with Earth blocking its view of the Sun, it’s due largely to the distances involved. Our Moon can completely block the Sun from our perspective, but we are only separated from each other by a few hundred thousand kilometres; from Mars, the Earth is very small and doesn’t cast much of a shadow. As a result, even the very slight difference in our orbital planes means that Mars still gets plenty of sunlight. On the other hand, when the Earth eclipses the Sun we minimize any excess light that might otherwise wash out the planet’s brightness.

The planar offset between the orbits of Earth and Mars.

If you’re unlucky enough to be under a bit of cloud cover on the night of the 14th, you can find Mars even more easily by looking for the full Moon. Directly above the Moon, sitting near the middle of the constellation Virgo, Mars will be shining brightly. Happily, the entire month of April should be prime viewing time for Mars. If April 8th or 14th don’t for you, feel free to pull out the amateur telescope (or just use your naked eyes) on any clear night this month.